So now we can move the Top Bar inside the inside navigation container using this PHP snippet:
add_action( 'after_setup_theme' , function() {
remove_action( 'generate_before_header' , 'generate_top_bar' , 5 );
add_action( 'generate_inside_navigation' , 'generate_top_bar' , 25 );
});
Adding PHP:
https://docs.generatepress.com/article/adding-php/
Then you will need this little bit of CSS to display the top bar over the menu:
.top-bar {
flex: 1 0 100%;
}